Multispecies Biofilms in Broiler and Pig Drinking-Water Systems: What a 2026 Field Study Found

The study and its design

The paper, 'Hidden threats: exploring biofilm communities in broiler houses and pig nursery units drinking water lines' (Van Rossum et al., BMC Microbiology, 5 March 2026; doi 10.1186/s12866-026-04790-6), sampled 15 broiler houses and 15 pig nursery units in Belgium between December 2022 and January 2024. At the end of each production round, after the animals had left and before any cleaning or disinfection, the team drained the lines and swabbed a 20 cm² area of the internal pipe surface into neutralising buffer, and took water samples from the source and from the drinking nipples. Samples were plated for total aerobic counts, faecal indicators and selected pathogens, isolates were identified, and 16S rRNA metabarcoding was applied to the biofilm swabs.

This is a descriptive survey of what accumulates in farm water lines under normal management. It was not an intervention study. No disinfectant was applied as part of the research and no comparison of cleaning or disinfection regimes was made, so it cannot say what removes these biofilms or how well.

What was found

Microbial load did not differ significantly between the two sectors: the median total aerobic count on the pipe surface was 3.6 log CFU/cm², roughly 4,000 culturable bacteria per square centimetre, at the end of a round. Enterococci, a faecal indicator, were detected in 80 per cent of all biofilm samples. Escherichia coli was found more often in broiler houses (47 per cent of samples) than in pig nurseries (27 per cent). The two dominant genera were Staphylococcus and Pseudomonas. Across both sectors Staphylococcus saprophyticus was the single most frequent isolate (10.6 per cent of all isolates). In broiler houses the next most frequent were Pseudomonas aeruginosa (5.6 per cent) and Stenotrophomonas maltophilia (5.3 per cent); in pig nurseries, Pseudomonas fluorescens (6.3 per cent) and Psychrobacter faecalis/pulmonis (5.5 per cent).

The finding with the most practical weight is the link between biofilm and the water the animals drink. Similar bacterial taxa were found in the water at the drinking nipples and in the biofilm on the water-contact surfaces, and the authors concluded that the drinking-water community depended not only on the source water but also on the biofilm in the system. In plain terms, water that enters a house clean can reach the nipple carrying organisms shed from the line, and the source-water result alone does not describe what the animals receive.

Why these communities are difficult

Farm drinking lines combine most of the conditions that favour biofilm: low flow and long dead-legs at the ends of lines, warm house temperatures, additives such as vitamins, acids, vaccines and medicines dosed through the water, and a mixed inoculum from source water, dust and animal contact. The organisms found are consistent with that: Pseudomonas species are strong matrix producers and are among the most disinfectant-tolerant environmental bacteria; Staphylococcus species and enterococci are robust and indicate faecal or skin contamination; Stenotrophomonas and Psychrobacter are opportunists that persist in wet, low-nutrient environments. Communities of this kind are more tolerant of any treatment than the single-species laboratory biofilms most efficacy data are generated on, a point made in detail in the mixed-species tolerance guide.

The authors also note what earlier Belgian work had shown: that the oxidiser- and acid-based cleaning and disinfection typically applied between rounds often fails to eliminate these biofilms, so that lines start each round already colonised. That observation concerns the regimes those farms were using; it is not a finding about any specific product.

What this does and does not mean for PT3 hygiene

What it establishes: farm drinking lines in ordinary commercial use carry substantial mixed-species biofilm at the end of a round; faecal indicators are common in it; and the biofilm contributes to what reaches the drinker. Line hygiene therefore belongs in the biosecurity plan, verification should sample the line and the nipple rather than only the source, and end-of-round cleaning needs to remove matrix, not just reduce counts in the flowing water.

What it does not establish: anything about chlorine dioxide. The study did not apply, measure or compare chlorine dioxide, chlorine, peroxide or any other agent. It provides no log-reduction, no contact time and no dosing information, and it says nothing about ChloroKlean products, which were not part of the research. Any statement of the form 'this study shows chlorine dioxide is effective against farm water-line biofilm' would be false. Where a site uses an authorised product for line cleaning (PT3 for the equipment, PT5 where the water animals drink is treated), the concentration, contact time and method come from that product's label and authorisation, and the evidence that it worked on that site comes from the site's own before-and-after sampling.

Evidence and uncertainty

Published biofilm studies are valuable for understanding mechanisms, but their conditions may not match a particular installation. Species, surfaces, deposits and operating conditions should be recorded when interpreting evidence.

For safety-critical systems, decisions should be documented through the relevant risk assessment and management plan.

Choosing the next question

A useful next step is to identify what is known, what is inferred and what needs verification. This avoids treating a general reference as a site diagnosis.

Where a product is considered, confirm the intended use, lawful GB BPR route and label directions independently of this educational guide.

Use this sequence to frame investigation and control; it is not a dosing protocol.

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